Freshly cut fruits and vegetables continue to respire after being picked, washed and cut, and need to be packaged in such a way that the oxygen and carbon dioxide transmission rates of the packaging matches the respiration rate of the produce. Each fruit or vegetable has its own respiration rate, thereby requiring a unique package.
Various combinations of polyolefin films have been used for making food packaging materials. For example, U.S. Pat. No. 5,500,284 discloses composite films especially suited for the production of bags to be used for solid and/or liquid products, and/or to preserve products that must be kept at low temperatures. The film consists of (A) a single- or multilayer bioriented film, where the single layer or at least one layer of the bioriented film is a crystalline propylene homopolymer, and (B) a single- or multilayer cast film wherein the single layer or at least one layer of the film is a layer of a composition including a propylene polymer such as a copolymer of ethylene with propylene and/or a C.sub.4 -C.sub.8 alpha-olefin.
U.S. Pat. No. 5,318,842 discloses a biaxially oriented film or sheet article comprising (A) a base or inner layer of a film of a C.sub.3 -C.sub.10 alpha-olefin homopolymer or a copolymer such as a copolymer of propylene and two different olefins selected from ethylene and C.sub.4 -C.sub.10 alpha-olefins, and (B) at least one layer of a broad molecular weight distribution propylene polymer, optionally containing another propylene polymer such as a a copolymer of propylene and at least two different olefins selected from ethylene and C.sub.4 -C.sub.8 alpha-olefins. The films are described as having improved stiffness and moisture vapor transmission properties compared to conventional film grade polyolefin resins.
U.S. Pat. No. 5,741,565 discloses a multilayer cast film comprising (A) at least one layer of a propylene homopolymer, copolymer, or terpolymer with ethylene and/or a C.sub.4 -C.sub.8 alpha-olefin, and (B) at least one layer of a propylene homopolymer, copolymer, or terpolymer with ethylene and/or a C.sub.4 -C.sub.8 alpha-olefin or a composition of a random copolymer of propylene with ethylene and/or a C.sub.4 -C.sub.10 alpha-olefin. The preferred film is made up of three layers in which (B) is placed between two outer layers of (A), or (A) is placed between two outer layers of (B). The films are especially useful for confectionery packaging.
There is still a need for a packaging material for fresh produce that can be tailored to match the gas transmission rate of a particular fruit or vegetable being packaged and thus meet the needs of individual producers.